Nuclear spin polarized rare gas production device and polarized rare gas production method using this

ABSTRACT

A device which can produce polarized rare gas further improved in polarization rate with the gas kept flowing, which has flat sheet surfaces facing each other via a gap, and which comprises, a flat-surface flow cell unit for allowing a mixture gas of rare gas and optically-pumping catalyst to flow in the gap there through in one diction thereof, a laser beam irradiation unit for applying a laser beam toward at least one of the flat sheet surfaces to apply an excitation light into the flat-surface flow cell unit, and a magnetic field application unit for allowing a magnetic line of force to pass through the laser beam-applied flat sheet surface perpendicularly or almost perpendicularly; and a method using this device.

TECHNICAL FIELD

The invention of the application relates to a device for producing raregas having high nuclear spin polarization rate, and a polarized rare gasproduction method using this. More particularly, the invention of theapplication relates to a device for producing rare gas polarized at thehigh rate of about several dozen percent or more, which is useful for aNMR device, and a polarized rare gas production method using this.

BACKGROUND ART

An important technical problem exists in that rare gas having highpolarization rate is achieved by a conventional NMR device.

Herein, the polarization means that the distribution of the number ofspins occupying an energy level of a nuclear spin of the atomic nucleuscorresponding to the state for the distribution to a main staticmagnetic field is extremely biased in comparison with the distributionat the thermal equilibrium.

Due to irradiation by circularly polarized excitation light to a mixedwith gases, wherein rare gas of the spin quantum number ½ ofxenon-129(¹²⁹Xe), helium-3(³He) or the like containing a monatomicmolecule having the nucleus spin is mixed with alkali metal steam suchas rubidium (Rb) and cesium (Cs), an electron of the ground state levelaccording to rubidium and the like is excited by photoabsorption,followed by being excited to the excitation state level and returning tothe ground state level, at one time, the electron likely transits to onelevel of the electron levels in the ground state level in which thedegeneracy is magnetically released by the magnetic field impressed fromthe outside; thereby the state having the high electron spin polarizeddegree of the rubidium molecule or the like is produced. The rubidium orthe like having the high polarized state is collided with the rare gasxenon or the like, and the high polarized state of the rubidium or thelike is moved to the nucleus spin system of the rare gas of the xenon orthe like in the process. Thereby, the rare gas having the polarizedstate is obtained. [W. Happer, E. Miron, S. Schaefer, D. Schreiber, W.A. van Wijngaarden, and X. Zeng, Phys. Rev. A29, 3092 (1984).]. Ingeneral, the process is called an optical pumping.

The following device is known as a conventional device for producing thepolarized gas. The mixture gas of a rare gas and alkali metal steam isenclosed in an optical reactive container, and the mixture gas isirradiated with the excitation light and the magnetic field is impressedto the mixture gas. For example, for the sake of using the polarizedhelium-3 having the high density as a neutron polarizer, the mixture gasof helium-3 gas and nitrogen, and an alkali metal are enclosed in acylindrical glass ampoule, and thereby the polarized gas is produced.[M. E. Wagshul and T. E. Chupp, Phy. Rev. A40, 4447 (1989).].

The following method is known as a device in which the polarized raregas of xenon-129 is applied to the nuclear magnetic resonancemeasurement (NMR) and the magnetic resonance imaging measurement (MRI).The method wherein NMR signal of the polarized xenon-129 is measured byusing xenon-129 and rubidium introduced to the cylindrical glasscontainer, and also the method of measuring the NMR signal of theproton-1 is measured whereby spin polarization is forwarded by applyingnucleus Overhauser effect to the proton-1 nucleus from the polarizedxenon-129 nucleus [D. Raftery, H. Tong, T. Meersmann, P. J. Grandinetti,L. Reven, and A. Pines, Phy. Rev. Lett. 66, 584 (1991) and G. Navon,Y.-Q. Song, T. Room, S. Appelt, R. E. Taylor, and A. Pines, Science 271,1948 (1996)], is known. It is also known the polarized xenon-129 isintroduced to an animal to measure the image of a cave such as a lung[M. S. Albert, G. D. Cates, B. Driehuys, W. Happer, B. Saam, C. S.Springer Jr., and A. Wishnia, Nature 370, 199 (1994) and U.S. Pat. No.5,545,396 (United States Patent)(1996)].

In any case, the operation for improving the polarization rate isperformed by entering the excitation beam from one direction in thestate where the rare gas or the like is stayed in a light responsecontainer. When the polarization rate rises, the rare gas or the like iscooled off, and is used as the neutron polarizer. The polarized rare gasis transported from the glass vessel to another container, and is usedfor NMR measurement or the like.

On the other hand, the following device and method are known as a deviceand a method for producing the polarized rare gas while making the gasflow. For example, xenon-129 of 1% is mixed with a buffer-gas ofhelium-4 gas of about 10 atmospheres, and the mixture is introduced to acylindrical glass container. The mixture is irradiated with theexcitation beam in parallel to the flow of the gas. That is, such anirradiation is carried out from the gas exit side of the container ofthe column bottom direction of the cylindrical glass container to theintroduction side. From the gas exit of the container, the polarizedmixed gas is induced in a dewar cooled off by a liquid nitrogen, andfollowing separating the polarized xenon-129 as a solid, and beingexhausted from a bentline. [B. Driehuys, G. D. Cates, E. Miron, K.Sauer, D. K. Walter and W. Happer, Appl. Phys Lett 69,1668 (1996).].

In addition, in the polarized rare gas production device that theinventors of the application have proposed, the polarized rare gas isproduced while making the gas flow safely near the normal pressure byusing the flow cell, and a nuclear magnetic resonance device is arrangedbackward thereof; thereby, NMR measurement can be performed in a shorttime without decreasing the polarization rate after polarized rare gasis continuously generated [Hattori, Hiraga, Nakai, Moriya, John M.Tracy, Japanese Unexamined Patent Application Publication No.11-309126].

However, in a device wherein the gas or the like is stayed in aconventional cylindrical glass and the gas is excited and polarized, thestrength of the excitation light, depending on the distance from theplane of incidence in the direction of the incidence, is exponentiallydecreased. The density of rubidium or the like in the cylindrical glasscontainer is optimized and determined to the part where excitation lightis strong; thereby, in a part which is away from the plane of incidenceand in which the excitation light is weak and occupies a considerablevolume.

Molecules such as xenon are moved to the part having high efficiency bydiffusion and convection, and thereby the decrease in the polarizationrate in the part having low excitation efficiency is dissolved. But, thedecrease in the polarization rate causes the decrease in the entireexcitation efficiency.

A problem exists in that in a conventional device which stays gas or thelike, and in which the gas is polarized, the polarized rare gas can notbe continuously generated, and time is required for taking out thepolarized gas to another container separately and carrying to the NMRdevice or the like, and the polarization rate is decreased in the meantime.

On the other hand, in a device which produces the polarized rare gaswhile making the gas flow, the following problems exists. Since thebuffer gas of the high pressure is introduced so as to reduce the los ofthe polarization rate due to the intermolecular collision of thepolarized xenon-129, there is a danger of handling a gas. In addition,the polarized xenon-129 solidified is heated again and must be taken outto a cool dewar, and the time is required for NMR measurement. Inaddition, the amount of xenon-129 polarized actually by the device isabout 5%.

Further, the excitation light is incidence only from one direction inthe device which the polarized rare gas is produced while the gas ismade to flow near the normal pressure by using the flow cell thatinventors of the application, have already proposed. Thereby a problemexists in that the polarization rate is decreased in a part away fromthe light source.

Therefore, the invention of this application dissolves the conventionalproblem described above. It is a subject of the invention of thisapplication that a polarized rare gas production device in which thepolarization rate is improved while the gas is safely made to flow, anda polarized rare gas production using the device are proposed by makingthe best use of the features of a device and a method that inventors ofthe application have proposed and improving the cellular shape and theexcitation light source. The subject of the invention of the applicationis to provide a nuclear magnetic resonance detection device which NMRand MRI measurement can be performed in a short time and withoutdecreasing the polarization rate after the polarized rare gas iscontinuously generated by such an improved device and a method, and NMRand MRI measuring method using the inventive device and enabling adetection in a ultra small area with the high sensitivity and shortenedmeasurement time.

DISCLOSURE OF INVENTION

This application has been made to solve the above problems. A nuclearspin polarized rare gas production device of the first inventioncomprises a flat-surface flow cell unit which has flat sheet surfacesfacing each other via a gap. In the gap of the flat-surface flow cellunit, wherein a irradiation area can make the best of the light powerdensity of the irradiated laser beam sufficiently, a mixture gas of raregas and optically-pumping catalyst flows in one direction.Simultaneously, an excitation light is applied into the flow cell unithaving the gap, and a magnetic field is applied so that a magnetic lineof force pass perpendicularly to the irradiation surface of the flowcell unit, wherein the excitation light is applied.

In a nuclear spin polarized rare gas production device of the secondinvention, the alkali metal such as rubidium (Rb) is selectivelydeposited on the surface opposite to the laser irradiation surface ofthe flat-surface flow cell unit to which the laser beam is applied so asto improve the vapor pressure of the alkali metal as theoptically-pumping catalyst, for example, the alkali metal such asrubidium (Rb), and the vapor pressure thereof is improved.

In a nuclear spill polarized rare gas production device of the thirdinvention, when the alkali metal such as rubidium (Rb) is selectivelydeposited on the surface facing the laser beam irradiation surface ofthe flat-surface flow cell unit, both rubidium (Rb) reservoir and theflat-surface flow cell unit an: in a high vacuum state of 10⁻⁵ Pa orless. The high temperature (for example, 150° C.) is maintained in thepipe containing the reservoir of the alkali metal such as rubidium (Rb),and the temperature of the surface facing the laser beam irradiationsurface of the flat-surface flow cell unit is maintained lower from themby about 50° C. to 200° C. (for example, about 50° C.).

In a nuclear spin polarized rare gas production device of the fourthinvention when the mixture gas of the rare gas and the optically-pumpingcatalyst flows to one direction in the flat-surface flow cell unit,thereof temperature (for example 400° C.) is able to maintain the vaporpressure of the optically-pumping catalyst by the arrangement and theaction of a temperature control unit, wherein such a vapor pressureprovides that the strength of the laser beam on the surface facing thelaser beam irradiation surface of the flat-surface flow cell unit maydecrease {fraction (1/10)} or more of the that on the laser beamirradiation surface.

In a nuclear spin polarized rare gas production device of the fifthinvention, the flat-surface flow cell unit is made of a material (forexample, quartz glass and sapphire) which substantially does not absorbthe laser beam applied, for example, the laser beam having thewavelength of about 795 nm (accurately, 794.7 nm:Rb), and does notdischarge water or volatile components from the inner wall offlat-surface flow cell unit heated when the polarized rare gas isproduced.

In a nuclear spin polarized rare gas production device of the sixthinvention, a magnet (for example, a permanent magnet and a Helmholtzcoil) having an air core structure is selected so as to secure a spacefor storing the flat-surface flow cell unit and the heating mechanismthereof.

In a nuclear spin polarized rare gas production device of a seventhinvention, when the mixture gas of the rare gas and theoptically-pumping catalyst flows to one direction in the flat-surfaceflow cell unit, the surface of the pipe inner wall, wherein the laserbeam is not irradiated and arranged in a downstream the part where theexcitation light is irradiated, is coated by a material which does notpromote the disappearance of the polarized rare gas, or is selected bythe material which does not promote the disappearance of the polarizedrare gas.

In a device of the eighth invention, a nuclear magnetic resonance deviceis arranged in the downstream of the flat-surface flow cell unit, andthe polarized rare gas is continuously generated to perform NMR measurein a short period of time without substantially reducing thepolarization rate.

In a device of the ninth invention, rubidium (Rb) of the alkali metal ispreferable as the optically-pumping catalyst. In a device of the tenthinvention, the quencher gas is flowed as a part of the mixture gas inthe fiat-surface flow cell unit.

In a method of the 11th invention, the polarized rare gas is produced byusing the above device.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration view illustrating the schematic configurationof the polarized rare gas production device of the invention of theapplication.

FIG. 2 is a configuration view illustrating the configuration of theflat-surface flow cell unit.

FIG. 3 is a configuration sectional view illustrating the configurationside of the flow cell by a metal and a glass.

FIG. 4 is a configuration view illustrating the arrangement of a highpower laser diode array.

FIG. 5 is a configuration view illustrating the arrangement of a highpower laser diode array which is different from FIG. 4.

FIG. 6 is a vapor pressure diagram of rubidium.

Reference numerals shown in Figures designate the followings.

-   1A, 1B: flat sheet surface-   2: gap-   3: metal-   4: glass-   5: Rb (rubidium)

BEST MODE FOR CARRYING OUT THE INVENTION

The invention of the application has the above characteristics, andhereinafter the embodiment will be described.

In the invention of the application, the cell of a nuclear spinpolarized rare gas production device has a large acceptance area. Theshape of the cell is improved to the plane type such that an excitationbeam source enters to the entire surface of the cell and the excitationbeam coincides with the half width of the light absorption ofoptically-pumping catalyst such as rubidium. The polarized rare gas canbe produced at the high polarization rate by irradiating with theirradiation beam using a high power (for example, 40 W) laser diodearray or the like, by applying a magnetic field, and also together byflowing the optically-pumping catalyst and the quencher gas is flowed inone direction in the flow cell unit, and wherein thereby the mixture gasof the rare gas of normal pressure. Measurements can be performed byusing NMR and MRI devices arranged behind the polarized rare gasproduction device.

Hereinafter, referring to the drawings, the embodiment of the inventionof the application will be described.

FIG. 1 is an overall schematic configuration view of a polarized raregas production device and a magnetic resonance detection device of theinvention of the application. Xe is shown as a rare gas. The gas is notlimited to the rare gas, and any known gases having a nuclear spin canbe used. Particularly, the gases having a nuclear spin of which the spinquantum number is ½, for example, the rare gases such as xenon-129 andhelium-3 are preferable.

In FIG. 1, the rare gas (Xe) is supplied from a steel cylinder. However,a container for supplying the rare gas is not limited to the steelcylinder, and any known gas supply devices such as a curdle, a houselinefrom a large size tank installed the outdoor and a low temperaturepreservation container can be used.

In the example shown in FIG. 1, nitrogen gas (N2) is used as quenchergas. The optically-pumping catalyst excited by the excitation beamirradiation has a sub-process of returning to a ground state by anon-radiative transition besides a main process of returning to theground state by a spontaneous emissions. The optically-pumping catalystcan be returned to the ground state in a short period of time byintroducing the quencher gas and transmitting the energy of the middlelevel of the optically-pumping catalyst to the quencher gas since theeasing time of the sub process is long. If the quencher gas does notexist in the cell, the polarized gas can be produced. However, thequencher gas preferably exists.

Hydrogen, nitrogen, organic gas having unsaturated bond, and organic gashaving the unsaturated bond (for example, acetylene, benzene, π-electroncompounds or the like) can be use for the quencher gas, andparticularly, the nitrogen is preferable. In FIG. 1, the quencher gas issupplied from a steel cylinder. However, a container for supplying thequencher gas is not limited to the steel cylinder, and any known gassupply devices such as a curdle, a houseline from a large size tankinstalled the outdoor and a low temperature preservation container canbe used.

Though the rare gas and the quencher gas are connected in the exampleshown in FIG. 1, gas for cleaning may be additionally connected. The gasfor cleaning removes impurities such as moisture and oxygen in a gaspipe and a cell before the rare gas and the quencher gas are introduced.In addition, the gas for cleaning is flowed to remove air from theoutside and moisture which is gradually desorbed from the inner wallwhile the rare gas and the quencher gas are stopped. The invention ofthe application can be executed even if the gas for cleaning is notused. However, it is preferable to use the gas for cleaning. The gas forcleaning can be supplied by the steel cylinder for nitrogen and argon orthe like, the curdle, and the houseline from the large size tankinstalled the outdoor.

In the example shown in FIG. 1, the rare gas and the quencher gas areintroduced into a flow cell after the pressure is lowered from a highpressure to the vicinity of a normal pressure by a pressure regulator.The pressure is preferably within the range of the atmosphere pressureto 10 atmospheres and particularly preferably the atmosphere pressure to3 atmospheres.

After the rare gas and the quencher gas pass through the pressureregulator, the flow rate of the rare gas and the quencher gas iscontrolled by a mass flow controller. Any commercially available gasflow adjusters such a flow meter, a flow meter with a needle valve, anorifice, a mass flow meter, and a mass flow controller can be used, andparticularly, the mass flow controller is preferable. Though the laminarflow region or the mixture region of the laminar flow and turbulent flowis used in the flow rate so as to prevent the decrease in thepolarization rate of the polarized rare gas by the collision to the gasintermolecular, the pipe wall and the cell inner wall, the laminar flowregion is particularly preferable.

The rare gas and the quencher gas which pass through the mass flowcontroller are introduced into the cell after passing through a gasdrying device and a gas highly purifying device and impurities areexcluded. Since moisture, oxygen, carbon dioxide, carbon monoxide, andother impurities decrease the efficiency of optical pumping by reactingwith the optical pumping agent, and ease spin system when colliding withthe polarized rare gas to decrease the polarization rate of the raregas, it is preferable that the gas introduced in the cell has highpurity.

When a high-purity gas is used, the gas drying device may be used thoughthe gas drying device is not necessarily acquired. The gas drying deviceremoves moisture contained in the gas. Though the gas can be refined byonly the gas highly purified device without using the gas drying device,it is preferable to use the gas drying device in view of extending theuse longevity of the gas highly purified device. The gas drying deviceis essential when only low purity gas can be used. Any known absorbentssuch as molecular sieve and a silica gel may be used for the gas-dryingdevice in the invention, and particularly, the molecular sieve heatedand dried previously is preferable.

The gas highly purifying device is used for excluding oxygen, carbondioxide, carbon monoxide, and other reactive impurities, and anyavailable commercially gas defectors such as a getter type, a resin typeand a metal complex type can be used for the invention.

In the example shown in FIG. 1, the rare gas and the quencher gas whichpass the gas highly purifying device are introduced into the cell. Rbfor the optical pumping agent, in a word, the optically-pumping catalystis previously moved to the cell. Herein, the optical pumping agent is amaterial having the following nature. When an electron of the groundstate level is excited by photo absorption, goes through the excitationstate level and returns to the ground state level by irradiating thecircularly polarized light excitation tight, the electron is likely tochange to one level of the electron levels in the ground state level inwhich the degeneracy is magnetically released by the magnetic fieldimpressed from the outside, and thereby the state having the highelectronic spin polarized degree can be produced. For theoptically-pumping catalyst in the invention of the application, analkali metal atom such as cesium, rubidium and sodium, a metal atom suchas a mercury atom, lead and cadmium, monatomic molecules of a metastablestate such as a mercury atom, lead and cadmium, monatomic molecules of ametastable state such as a helium atom of a metastable state generatedby electric discharge, and polyatomic molecule such as an organicradical and an inorganic radical may be used.

In the method for introducing the optical pumping agent, beforehand, theoptical pumping agent is transported to the surface facing the opticalirradiation surface of the polarized flow cell unit from a containerstow the optical pumping agent by using the temperature difference undera vacuum condition, and it is preferable that the rare gas and thequencher gas are mixed while the optical pumping agent is evaporated byheating.

For the sake of preventing the optical pumping agent in the invention ofthe application from segregating by the inhomogeneous temperaturedistribution, the container storing the optical pumping agent is cooledwhile irradiating light. It is preferable that the entire cell ismaintained at a uniform temperature. It is preferable to determine thetemperature in consideration of the saturated vapor pressure so as tocontrol the density of the optical pumping agent.

FIG. 2 is a plan view illustrating the flat-surface flow cell unit ofthe polarized rare gas production device in the invention of theapplication and an enlarged sectional view thereof. It consists of apair of flat sheet surfaces (1A), (1B) which are supported by a sidewalland are arranged opposite to each other in upper and lower, and a gap(2). It is preferable that the flat-surface flow cell unit has thefollowing structure: (1) the acceptance area is enlarged as much aspossible to make the best use of the strength of the light source forthe excitation light and to efficiently generate exited state ofrubidium or the like; (2) the thickness of the flow cell unit is thin soas to limit such that the mixed gas exist in only the area in which thebeam entering from the acceptance area is absorbed by rubidium or thelike in the flow cell unit and the strength of the beam is decreased andbecomes {fraction (1/10)} of the strength at entering; (3) the entirecell is made of a material which can be heated at 200° C. or more so asto desorbs water molecules or the like adsorbed to the cell inner walleasy; (4) the magnetic field application unit is arranged such that thedirection of the incidence of light is coincided with or almostcoincided with that of the magnetic line.

Metals such as a surface treated stainless steel, tantalum, molybdenum,platinum, rhenium, titanium, tungsten, zirconium and copper, a glasssuch as quartz may be for the material of the flow cell unit. A part orthe whole of the cell has preferably a window for an optical incidence.Quartz and sapphire, which have excellent permeability, can be used forthe window.

FIG. 3 is a sectional view illustrating configuration view of a cellhaving a gap (2) made of a metal (3) and a glass (4). Rb (5) isdeposited on the side of the metal (3).

FIGS. 4 and 5 are configuration views illustrating the arrangement of ahigh power laser diode array of the invention of the application as aplan view (A), a side view (B) and a front view (C). A lamp and a laseror the like can be used for an excitation light source, andparticularly, the laser diode is preferable. A ¼ wavelength plate can bearranged in front of the excitation light source so as to converting alinearly polarized light into a circularly polarized light. A lensobtained by combining by a concavoconvex cylindrical lens may be usedfor an expander.

For example, preferably, the diode array is a linear array having thesame length as that of the direction of the flow of the flow cell.

For example, as shown in FIG. 1, in the invention of the application, amagnet having an empty core structure such as a permanent magnet or thelike is used for the magnetic field application unit. In the exampleshown in FIG. 1, the magnet is arranged such that the direction of theincidence of light is coincided with that of the magnetic line. Thedirection of the incidence of the excited light is arranged in parallelwith or approximately in parallel with that of the magnetic line so asto perform the optical pumping. It is the largest effect for improvingthe polarization rate while the gas is flowed that the direction of theflow of the gas is vertical or almost vertical to both the incidencedirection of excited light and the magnetic line. Therefore, it is anespecially preferable structure in the invention of this applicationthat the excitation light is vertically irradiated to the directionwhere the gas contained in the flow cell is circulated, and that themagnetic line pa; vertically to the excitation light irradiation surfaceof the flow cell.

As shown in FIG. 1, the rare gas polarized by the cell is introducedinto a rear magnetic resonance detection device, and the magneticresonance detection measurement is performed. The magnetic resonanceimaging apparatus of an inductive detection type of a pulse method, anoptical microscope device detecting photo detection NMR tinder RFirradiation, or force detector type of a scanning probe microscopedevice using the principle of AFM or the like can be used for themagnetic resonance detection device used herein.

If a pulse type inductive detection method is applied in a conventionalstaying type rare gas polarized device, a problem ems in that xenon 129having the long easing time is saturated. However, since the polarizedrare gas molecules related to the measurement are subsequentlycounterchanged in the magnetic resonance detection device of theinvention of the application, the nuclear magnetic resonance signal canbe measured without receiving the influence of saturation.

EXAMPLE

Then, example is shown below, and the invention of the application willbe described. Of course, the invention is not limited to the followingexample.

In the example, the device illustrated in FIG. 1 is used.

Xenon (purity: 99.95%) of a natural isotopic ratio manufactured byNippon Sanso (xenon-129:26.44% content) is used for the rare gas, andnitrogen gas of S grade (purity: 99.9999%) manufactured by Nippon Sansois used for the nitrogen gas. Each flow rate is controlled by a valveand mass flow controllers (trade name: M-100-11C, M-310-01C,manufactured by MKS Corporation). The gases are then mixed in a line,and are introduced into a flat-surface flow cell unit placed in apermanent magnet having an air core structure. At this time, the cell iscontrolled at the temperatures of about 150 to about 300° C. by a hotwind blowing heating device. In the flat-surface flow cell unit,rubidium (Rb) may be previously deposited as described in FIG. 3. Whenboth the rubidium reservoir and the flow cell unit are in a high vacuumof 1×10⁻⁵ Pa in the deposition, the temperature of the flow cell unit isset such that the temperature of the flow cell unit is about 80° C.,lower than the that of the reservoir and the pipe.

The mass flow controller is use for controlling the flow rates of therare gas and the reactive control nitrogen in the flow cell. As themaximum flow rate and the minimum control flow rate of the rare, 10SCCM,0.2SCCM and 1.0SCCM, 0.02SCCM are used respectively.

A stainless steel 304 pipe of which one end is sealed and which has theoutside dimension of 12 mm and the thickness of 0.5 mm is used for therubidium reservoir. Rubidium (purity: 99.99%) manufactured by FuruuchiChemical Co., Ltd. is used. The rubidium is inserted into the reservoiras a glass ampoule. A vacuum exhaust is performed for about two daysuntil an attainment pressure is obtained by a vacuum exhaust device withan oil diffusion pump of the attainment pressure of about 10⁻⁷ Pa. Atthis time, a tape heater is fix to around the rubidium reservoir, and isheated up to about 100° C. Impurities such as the water adsorbed to thecell inner wall and the outside of the glass ampoule are removed. Thetape heater of the rubidium reservoir is removed and is returned to theroom temperature.

The hot wind blowing heating device is used for equalizing thetemperatures of the all part containing the pipe where the rubidiumvapor between the rubidium reservoir and the flow cell exists, and thetemperature is controlled by a temperature controller within ±1° C. of aset value. Since the rubidium vapor pressure in the flow cell changes byvariations in temperature, the vapor pressure is segregated when the lowtemperature part exists even in the part and it is difficult to controlthe rubidium vapor pressure. Thereby, it is necessary to maintain thewhole uniformly. The mixture gas which comes out the flow cell and ispolarized is cooled naturally, and the rubidium vapor is excluded.

The flat-surface flow cell has the internal width of 70 mm in thedirection of the now of the gas, the internal width of 50 mm in thedirection vertical to the flow, and the respective outside sizes of 80mm and 60 mm, and is made of quartz glass. The length of theflat-surface flow cell is longer than that of the illuminated part ofthe laser diode of 60 mm only by about 10 mm. The gap in the part wherethe gas flows is 1 mm, and the gap is adjusted such that the gap is{fraction (1/10)} or les of amount of light incident on the surface ofthe silica glass tube at the following conditions, and the gap becomesuniform over the length of 70 mm.

A linear array assembly of the laser diode on which the illuminated parthas the length of 60 min is set. The ¼ wavelength plate in front of eacharray is set, and thereby the linear polarized light is converted intothe circularly polarized light. The irradiation area and the arrangementare determined by a beam expander such that the circularly polarizedlight makes the best use of the beam extension angles (5.5 degrees and35 degrees) of the laser diode.

The laser diode array (LD) assembly has a center oscillation wavelengthof 794.7 nm. The laser diode array (LD) assembly of which the entirelength of the luminescence part is set to 60 mm is arranged on a tabularheat sink. The entire output of the assembly is 150 W, and the beamextension angle in the direction vertical to the direction of the flowis 35 degrees.

The ¼ wavelength plate used has the size in which the front surface ofone unit of LD is covered with one sheet thereof.

The permanent magnet is composed of two groups of meet which is arrangedin small tabular permanent magnets at respective upper and lower steps,and the strength of the magnetic field in the gas flow part of the flowcell is set to 0.01 teals (T).

As shown in FIG. 1, the amount of the polarized rare gas generated ismeasured from NMR signal strength of xenon-129 by using a magneticresonance imaging apparatus arranged downstream of the glass tube.Herein, devices of one's own making such as an electromagnet for staticmagnetic field, a coil for RF irradiation, a RF amplifier and a NMRdetecting coil and an amplifier are used for the magnetic resonance ingapparatus which is used for the measurement. Each part is adjusted suchthat the frequency of a detector is set to 3.5 MHz with proton andxenon-129.

Next, the polarized rare gas is generated by the following experimentprocedures. First of all, the valve of the vacuum line is opened forpreparing, and the vacuum exhaust is performed for about two days.Thereby, the pipe containing the flow cell is dried and is highlypurified. At this time, the gas lines other than the rubidium reservoirmm rolled by a ribbon heater, and are controlled at about 150° C. Astainless steel 304 pipe of the rubidium reservoir of the wall thicknessof 0.5 mm is clipped by a clamp from the outside; thereby, the internalglass ampoule is crushed, and the rubidium metal is filled in thereservoir. Then, the power supply of a thermostatic chamber controllingthe temperatures of the rubidium reservoir and the flow cell for opticalpumping is turned on and such a control is started at 94° C. As shown inFIG. 5, the vapor pressure of the rubidium is 10⁻⁸ Torr at 0° C., about10⁻⁵ Torr at 38.89° C., and 10⁻⁴ Torr at 94° C. In this example, thevapor pressure of the rubidium is set to 10⁻² Torr at 200° C.

Afterwards, the valve of the nitrogen line for dryness is shut, and thevalves of the xenon for light response and nitrogen are openedrespectively. The flow rates are respectively adjusted to 6SCCML and0.1SCCM by adjusting the mass flow controller. In this case, the staytime of the mixture gas in the cell is estimated for about 30 seconds.After the mixture gas of the xenon and nitrogen reaches the NMRdetector, the signal level is recorded.

The power supply of the laser diode (LD) is turned on, and the flow cellis irradiated with the circularly polarized light. The output signal ofthe detector is recorded. The power supply of the laser diode isintermitted for confirmation, and the output signal of the detector atthis time is recorded. On the other hand, the glass tube having the samesize as that of the glass tube used at the experiment of the polarizedxenon is filled with water having a known magnetic susceptibility, andthe glass tube is made to the reference of the polarization ratecalculation by measuring the signal obtained when inserted in thedetector.

The ratio of the size of the spin magnetization contributing to thesignal in the proton at the thermal equilibrium and xenon-129 of thepolarization rate of 100% is 1:10000. By using such a relation, thepolarization rate of xenon-129 can be estimated from the NMR signalstrength obtained by the gyromagnetic ratio of proton and xenon-129, andfrom the experiment using the same volume of water and polarized xenon.The maximum value of polarization rate of the xenon-129 is 40 percentaccording to the signal strength and the NMR signal strength obtained bythe configuration using the water having the same volume.

The description is summarized as follows. The signal strength of thepolarized xenon generated is monitored and the output wave pattern ofthe magnetic resonance detection device changes reversible correspondingto the change of the time of strength of the diode laser beam when thepolarized rare gas production device is irradiated with the high powerdiode laser beam. That is, it is confirmed that the amount of generationof the polarized xenon can be controlled by the increase and decrease ofstrength of the diode laser beam or the intermission, in other words,the sensitivity of the NMR signal of xenon-129 is reinforced about10,000 times or more by irradiating the diode laser beam.

INDUSTRIAL APPLICABILITY

The following effects can be achieved as described above in detailaccording to the invention of the application.

That is, the polarized rare gas can be produced safely and continuouslyby circulating the mixture gas of a rare gas of the low pressure andoptically-pumping catalyst to one direction in the flat-surface flowcell unit, and by irradiating the excitation light and applying themagnetic field in the flow cell. The polarization rate can bedramatically improved by efficiently irradiating the excitation light inthe flow cell whereby the high power laser diode array arranged straightis used for the excitation light source.

Furthermore, the polarized rare gas production device is arranged inforward of the magnetic resonance imaging apparatus, whereby thepolarized rare gas continuously generated is coated so as to decreasethe easing of the nuclear spin by a magnetic interaction with the pipeinner wall; thereby, the polarized rare gas continuously generated canbe introduced into the magnetic resonance imaging apparatus in a shortperiod of time without causing the decrease in polarization rate bytransportation to another container, and the magnetic resonance imagingmeasurement can be performed.

Moreover, since the polarized rare gas is used for detection nucleus,the detection sensitivity of the NMR signal can be improved, and it isenabled that the measurement time of the NMR spectrum and the MRI imagemeasurement is greatly shortened, and also that the detection area maybe extremely miniaturized.

1. A nuclear spin polarized rare gas production device comprising: aflat-surface flow cell unit which has flat sheet surfaces facing eachother via a gap, and allows a mixture gas of rare gas andoptically-pumping catalyst to flow in the gap in one direction thereof;a laser beam irradiation unit for applying a laser beam toward at leastone of the flat sheet surfaces to apply an excitation light into theflat-surface flow cell unit; and a magnetic field application unit forallowing a magnetic line of force to pass through the laser beam-appliedflat sheet surface perpendicularly or almost perpendicularly; wherein analkali metal of the optically-pumping catalyst is deposited inside thefacing flat sheet surface of the side opposite to the flat sheet surfaceof the flat-surface flow cell unit to which the laser beam is applied.2. (canceled)
 3. The nuclear spin polarized rare gas production deviceaccording to claim 1, wherein the deposition of the alkali metal isformed at the state where the temperature of the flat sheet surface ofthe flat-surface flow cell unit on which the alkali metal is depositedis lower than the temperatures of the reservoir of the alkali metal andinside the pipe thereof by 5° C. to 200° C. at the state where both thereservoir of the alkali metal and the flat-surface flow cell unit are ina high vacuum of 10⁻⁵ Pa or less.
 4. The nuclear spin polarized rare gasproduction device according to claim 1, wherein a temperature controlunit is provided, which can maintain the vapor pressure of theoptically-pumping catalyst reduced exceeding {fraction (1/10)} of thestrength of the laser beam at the facing flat sheet surface side to thestrength of the laser beam of the flat sheet surface side of theflat-surface flow cell unit to which the laser beam is applied.
 5. Thenuclear spin polarized rare gas production device according to claim 1,wherein the flat-surface flow cell unit is made of a material which doesnot absorb the laser beam applied substantially, and does not dischargewater or volatile components.
 6. The nuclear spin polarized rare gasproduction device according to claim 1, wherein the magnetic fieldapplication unit has an air core structure.
 7. The nuclear spinpolarized rare gas production device according to claim 1, wherein atleast the inner wall of the pipe to which the laser beam is not appliedin the downstream of the flat-surface flow cell unit is made of amaterial which does not promote the disappearance of the rare gaspolarized.
 8. The nuclear spin polarized rare gas production deviceaccording to claim 1, wherein a nuclear magnetic resonance device isarranged in the downstream of the flat-surface flow cell unit, and thepolarized rare gas is continuously generated to perform NMR measure in ashort period of time without reducing the polarization ratesubstantially.
 9. The nuclear spin polarized rare gas production deviceaccording to claim 1, wherein the optically-pumping catalyst is rubidium(Rb) of the alkali metal.
 10. The nuclear spin polarized rare gasproduction device according to claim 1, wherein quencher gas is flowedas a part of the mixture gas in the flat-surface flow cell unit.
 11. Anuclear spin polarized rare gas production method comprising the stepof: producing the nuclear spin polarized rare gas from the rare gasflowed in the flat-surface flow cell unit in the polarized rare gasproduction device according to claim
 1. 12. A nuclear spin polarizedrare gas production method comprising the step of: producing the nuclearspin polarized rare gas from the rare gas flowed in the flat-surfaceflow cell unit in the polarized rare gas production device according toclaim
 3. 13. A nuclear spin polarized rare gas production methodcomprising the step of: producing the nuclear spin polarized rare gasfrom the rare gas flowed in the flat-surface flow cell unit in thepolarized rare gas production device according to claim
 4. 14. A nuclearspin polarized rare gas production method comprising the step of:producing the nuclear spin polarized rare gas from the rare gas flowedin the flat-surface flow cell unit in the polarized rare gas productiondevice according to claim
 5. 15. A nuclear spin polarized rare gasproduction method comprising the step of: producing the nuclear spinpolarized rare gas from the rare gas flowed in the flat-surface flowcell unit in the polarized rare gas production device according to claim6.
 16. A nuclear spin polarized rare gas production method comprisingthe step of: producing the nuclear spin polarized rare gas from the raregas flowed in the flat-surface flow cell unit in the polarized rare gasproduction device according to claim
 7. 17. A nuclear spin polarizedrare gas production method comprising the step of: producing the nuclearspin polarized rare gas from the rare gas flowed in the flat-surfaceflow cell unit in the polarized rare gas production device according toclaim
 8. 18. A nuclear spin polarized rare gas production methodcomprising the step of: producing the nuclear spin polarized rare gasfrom the rare gas flowed in the flat-surface flow cell unit in thepolarized rare gas production device according to claim
 9. 19. A nuclearspin polarized rare gas production method comprising the step of:producing the nuclear spin polarized rare gas from the rare gas flowedin the flat-surface flow cell unit in the polarized rare gas productiondevice according to claim 10.